Country singer Keith Urban performed before 18,000 fans at the Xfinity Center in Mansfield on July 26, but itís not his music that is making headlines. Instead, itís the raucous party atmosphere that left nearly 100 people sick or in protective custody. Shortly before 9 p.m., less than two hours into the show, Mansfield declared a "mass casualty event" at the venue.By 10:30 p.m., two life support ambulances had to be called to the scene, in addition to many other emergency vehicles. Foxboro, Easton, Norton, Plainville and North Attleboro all sent emergency crews to the scene.Urban fan Savannah Feder, 29, of Framingham, said the hardcore partying before the show forced her to leave early."There were two extremely drunk girls beside my husband who kept jumping over the railing," she said. "Another man behind us climbed over the railing and kicked me really hard. He slurred an, ĎIím sorry,í but later spilled his beer on my husband. At that point, my husband wanted to leave. I remember looking up at the lawn and it was packed. I saw the ambulance people go by with boards twice before we left."Town Manager William Ross met with emergency officials on Monday to discuss what to do about the trouble at the Urban concert and how to prevent it a repeat. He said there would be more police and emergency workers at future shows."We will do what is necessary to protect the public because ultimately that is our responsibility," he said.Country music crowds can be rowdy. In August 2012, more than 100 people were arrested and nearly 500 were taken into protective custody at a country music festival at Gillette Stadium in Foxboro. In 2011, a 19-year-old was brutally beaten at a Tim McGraw show in Mansfield."From my understanding, Keith Urban generally attracts an older crowd, but there were a lot of young people who were taking mind-altering substances, mainly alcohol, and we donít really know why it happened at this show compared to other shows," Ross said."Country shows have proven to be the most difficult for us," Ross said. "The problems start in the parking lot, then carry on inside. The lawn area is a specific problem because it is tightly packed and on a slope."Two more country music shows are scheduled this season, Brad Paisley on Aug. 23 and Miranda Lambert on Sept. 6. But itís not just country.Saturdayís concert was held two years to the day after two people died and 45 were arrested at a rave at the Comcast Center, as Xfinity Center was called at the time. Just last month, two dozen people were treated for drug overdoses at an electronic dance music show at TD Garden in Boston.